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September 2003
 Re: units in sbml l2v3 04 Jun '07 15:38 Hello Nicolas, hello all, On Monday 04 June 2007 22:58:41 Nicolas Le Novere wrote: > > I don´t see why the "old way" should not allow a correct calculation. I > > understand that square inches look nicer with the "new way" but that does > > not > > make the "old way" incorrect. > > > > in = 2.54 * 10^-2 * m > > > > old way : sqin = 2.54^2 * 10^-4 * m^2 > > Sven, here is the misunderstanding. In the old way, you do not have the > first exponent. Your example is too simple. Sorry, I was just lazy. I didn´ t want to actually calculate 2.54^2. I know that I should have written : old way: sqin = 6.4516 * 10^4 *m^2 And as I said I see that this one looks nicer with the "new way". > Let's take another one, more > explicit (I hope): a density of molecule expressed in micromole per square > inches: > > > > > > > > > > > old way: > > mole x 10E-6 x 0.254 x (metre)^(-2) > > new way: > > mole x 10E-6 x (0.254 x metre)^(-2) > > The first one is wrong. The second is right. (minor correction: it should be 0.0254, not 0.254, but that is not the problem) It is quite obvious that if you encode a unit in sbml using the "new way" and then interprete it the "old way", as you did, the result will be wrong. If you encode the old way, and then interprete the old way, it will be correct: sbml code old way: old interpretation: mole x 1e-6 x 0.00064516 m^(-2) new interpretation: mole x 1e-6 x (0.00064516 m)^(-2) The first is right, the second is wrong. Which is understandable, since it was encoded the old way. And I can see that in this example the new way looks more intuitive. What I really do not get at all is: Why do you consider the old interpretation "wrong"? It´s just a mathematical definition. Old: Unit=multiplier*10^scale*baseunit^exponent New: Unit=(multiplier*10^scale*baseunit)^exponent Both are valid definitions. May be one is more convenient, may be one is more fit for calculations, may be one is more adapted to what people expect. Perhaps one is more appropriate for manual calculations, the other for automatic handling. But certainly non of them is "wrong". You know which definition I prefer. But I´ll try to be fair: I think the new definition is definitely better for displaying units that involve areas or volumes defined in imperial length units. And (after reading the postings) it seems it matches the expectations of some sbml experts (which is a strong argument). I think the old way was better actually doing calculations without loosing accuracy due to floating point operations, and for easier software development. -- Sven Sahle Bioquant, Universität Heidelberg ____________________________________________________________ To manage your sbml-discuss list subscription, visit https://utils.its.caltech.edu/mailman/listinfo/sbml-discuss For a web interface to the sbml-discuss mailing list, visit http://sbml.org/forums/ For questions or feedback about the sbml-discuss list, contact sbml-team@caltech.edu.

SubjectPosterDate
units in sbml l2v3 Ralph Gauges30 May '07 06:21
Re: units in sbml l2v3 Mike Hucka01 Jun '07 14:07
Re: units in sbml l2v3 Sven Sahle01 Jun '07 16:36
Re: units in sbml l2v3 Mike Hucka03 Jun '07 11:46
Re: units in sbml l2v3 Sven Sahle04 Jun '07 08:36
Re: units in sbml l2v3 Stefan.Hoops04 Jun '07 11:28
Re: units in sbml l2v3 Sven Sahle04 Jun '07 13:06
Re: units in sbml l2v3 Ralph.Gauges04 Jun '07 13:27
Re: units in sbml l2v3 Nicolas Le Novere04 Jun '07 13:58
Re: units in sbml l2v3 Nicolas Le Novere04 Jun '07 14:42
Re: units in sbml l2v3  Sven Sahle04 Jun '07 15:38
Re: units in sbml l2v3 Nicolas Le Novere05 Jun '07 00:47
Re: units in sbml l2v3 Sven Sahle05 Jun '07 03:59
Re: units in sbml l2v3 Mike Hucka06 Jun '07 23:19
Re: units in sbml l2v3 Mike Hucka06 Jun '07 23:42
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